Firstly, may I add to the many messages of condolence to the families of the people on the ground, the helicopter flight crew, and the Police Force involved.
We have the best people in the World investigating the accident; the AAIB. Please let them do their job.
I had the pleasure of meeting Pete and his lovely wife in October this year.
Pete may be new to PPrune but he is most certainly not new to flying helicopters; he would most likely put a reasonable number of you 'experts' to shame, a true professional.
Pete (and he will correct me if I am mistaken) is referring to the use of available stored energy that the pilot can call upon to prevent Low RPM Rotor Stall should they find themselves in a situation where their single engine has failed.
Cruise Flight:
With a low inertia rotor system, the least amount of energy stored in the helicopter and which is immediately available to the pilot, is that stored in the main rotor (kinetic). Hence the rotor RPM decays quickly.
However, the most amount of stored energy available is stored in the forward airspeed and this is available to the pilot instantly. The pilot can call on this energy to prevent rotor rpm decay during the entry into autorotation by applying aft cyclic.
In fact if I take an R22 at a 90kt IAS cruise flight condition I have some 8 seconds of stored kinetic energy that would allow me plenty of time to lower the collective (Note: it does not change the intervention time). It is there…. so use it.
For those that say 'well I might need it for range' then range is of no use to you if you are a brick! The primary task is to establish autorotation. If you fly defensively you will reduce the requirement for range autos (I am talking single engine operation).
In the hover the pilot should lower the collective lever and allow the helicopter to descend and regain the RRPM before applying fwd cyclic for airspeed; the positive effect of increasing the airspeed is an increase in RRPM.
However there is a negative first, and that is a reduction of RRPM. So if the pilot should apply fwd cyclic before the RRPM has recovered this will add to their problems.
There is more but I am due out to dinner.
R